Phosphors are lambertian emitters, emitting light in all directions. In traditional LED implementations, phosphor is applied on the LED chip, in a silicone matrix in proximity to the LED or to the outside of an LED dome or other LED packaging. A dome may be applied to an LED chip coated with phosphor to control the light beam angle (shape) from lam bertian to a very narrow spot. Such devices range from hemispherical lenses to T-5 mm (T 1¾) aspheres. One conventional system for producing white light LEDs, for example, is constructed with pump blue/UV LED chips and a proximate mixture of phosphor in a binding matrix such as silicone. The term “goop in a cup” is used to describe LEDs with flat or very nearly flat phosphor and silicone mixture over a blue pump. In remote phosphor systems, phosphor is applied away from the chip on the outside of a dome or inside of a hemispherical shell to increase converting efficiency. However, an additional lens may be needed to control light beam shape. The GE VIO employs the remote phosphor solution.
Current systems suffer efficiency losses due to heating of the LED chip and the phosphor particles. Additionally, many current systems require secondary optics or additional lenses to shape the light emitted from a dome or phosphor coated LED into a desired beam angle. The coupling of a lens to a dome causes efficiency losses of approximately 10% or greater. Furthermore, current systems suffer conversion losses when multiple color phosphors are used due to cross-excitation. For instance, a red-emitting phosphor may absorb down-converted light from a green-emitting phosphor instead of the pump wavelength, thereby introducing further losses.